centrist (n.)

1872, from French centriste, from centre (see center (n.)). Originally in English with reference to French politics; general application to other political situations is by 1889.

Where M. St. Hilaire is seen to most advantage, however, is when quietly nursing one of that weak-kneed congregation who sit in the middle of the House, and call themselves "Centrists." A French Centrist is--exceptis eoccipiendis--a man who has never been able to make up his mind, nor is likely to. ["Men of the Third Republic," London, 1873]